When hard-partying Mary Larson had her first snort of cocaine in the late ’70s, she quickly became hooked. She eventually lost her job and left her husband, two preteen sons and two-story Concord, California, home. Her younger son knelt and sobbed, begging her not to leave. But he couldn’t have been further from her mind. I don’t want to live here, she thought. I want to get high!

Larson hustled for nearly 10 years throughout the San Francisco Bay Area to feed her $500-a-day habit. She robbed up to five Safeway supermarkets each day and worked as a prostitute at night. Her lowest point came in 2006, when a group of police officers chased her and hurled her to the ground after she stole a bottle of liquor. “I felt like a dog,” she said. “I’m thinking, ‘Oh my God, I can’t do this anymore.’” The whole time, she thought of her youngest son, kneeling and weeping in front of their house.

So Larson checked herself into HealthRIGHT 360, a San Francisco-based drug-rehab program that offers medical care, behavioral therapy, education and employment services. “I was like a sponge,” she said. “I wasn’t there to play anymore.” And her perseverance paid off. Today, the 58-year-old is an events director at HealthRIGHT 360 — and her sons call her every night. “I’m the happiest person,” she said.

The idea is that when addicts no longer get a rush from cocaine, they’ll stop using it….

A vaccine “could be used for any addictive molecule,” said study leader and physician Ronald Crystal, whose group is also developing a nicotine vaccine. Other researchers are working on vaccines to block the effects of phencyclidine (PCP), as well as opioids like heroin, methamphetamine and the prescription pain medication fentanyl. The opioid epidemic has only continued to wreak havoc on families and communities in the U.S., with the Centers for Disease Control and Prevention estimating that an opioid overdose kills 91 Americans every day.

But some remain skeptical. Addiction vaccines have produced mixed results in clinical trials, and pharmaceutical companies are hesitant to fund them. And if cocaine no longer has an effect, an addict might just turn to another drug. After all, these vaccines are targeting specific substances that trigger addiction — not the condition itself.

A vaccine exposes the immune the system to a harmless amount of the pathogen it’s designed to protect against. The immune system recognizes the pathogen as foreign and churns out proteins called antibodies that attack it if it reappears.

The idea for a cocaine vaccine came to Crystal as he was walking past a Manhattan newsstand several years ago. A headline read, “Addiction: We Need a Vaccine.” He wondered — could he make a vaccine against an addictive molecule, like cocaine?

Of all the illegal drugs, cocaine is especially dangerous. Both the inhaled powder form and smoked crack cocaine account for roughly one-third of drug-related emergency room admissions. And unlike with heroin or prescription painkillers, there are no medications specifically approved to curb cocaine addiction. So far, only behavioral therapy has been shown to help — but not for everyone. Combining therapy with a vaccine might be more effective.

Addictive molecules like cocaine are too tiny for our immune system to detect. So Crystal’s group tethered a particle that mimics the structure of cocaine onto larger cold-virus proteins. When the vaccine is injected into an animal, its immune system recognizes the viral proteins as foreign and triggers an attack against both the proteins and the attached cocaine look-alike.

We’re excited. The fact that it works very well in monkeys is a real suggestion that it might work well in humans

Ronald Crystal, M.D., Weill Cornell Medical College

Cocaine is a molecule that inhibits a protein called the dopamine transporter. This protein usually shuttles dopamine — aka the “feel-good” neurotransmitter — away from the space between nerve endings to be recycled, but when that process gets interrupted by cocaine the body ends up with a surplus of dopamine, which produces an intense high. To measure this effect, the researchers hooked a scannable tracer onto the transporter protein.

Once the vaccine worked in mice, researchers next tested it in rhesus macaque monkeys, whose biology is much closer to that of humans. When they injected the monkeys with cocaine, the results were stunning.

Brain scans of unvaccinated monkeys showed a drop in the activity of the tracer: In these subjects, cocaine continued to inhibit the dopamine transporter. But in vaccinated monkeys, Crystal’s group saw that the antibodies had attacked the cocaine, leaving the dopamine transporter protein and the attached tracer untouched.

To produce a high, cocaine needs to block 47 percent of the transporter molecules — but it blocked only 20 percent in vaccinated monkeys. And when given a choice, those vaccinated monkeys chose M&M’s over cocaine, since the drug no longer gave them a rush.

“We’re excited,” Crystal said. “The fact that it works very well in monkeys is a real suggestion that it might work well in humans.” He and his colleagues are now recruiting cocaine addicts for a clinical trial of the vaccine.

Crystal noted that a vaccine won’t be a silver bullet and will most likely be used alongside behavioral therapy. HealthRIGHT 360 CEO and recovered heroin addict Vitka Eisen agreed. “People also need jobs, safe housing … and social support,” she said. “Medication can be really helpful as part of a toolbox.”

The Salvation Army’s drug and alcohol rehabilitation, called ARP, is gritty, painful and has more rules than boot camp.

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But Stanford University psychiatry professor Keith Humphreys isn’t so sure. He cited a 2009 cocaine vaccine trial in which only 38 percent of vaccinated patients developed immunity. Plus, Big Pharma has shown little interest in such vaccines, since many doctors don’t view addiction as a legitimate medical condition.

It’s also possible that vaccinated cocaine addicts might just get their fix elsewhere. “I would have probably just switched addictions,” says Larson. “If you’re an addict, and you’re not already using, you’re looking for something else.”

But that doesn’t necessarily mean scientists like Crystal should stop trying. A successful clinical trial could make physicians — and Big Pharma — take notice. For addicts who continue to relapse, the potentially lifesaving treatment can’t come soon enough.

This story has been updated since its original publication on February 25, 2014.